The ALD (Atomic Layer Deposition) process is useful for the creation of thin films, as described by M. Ritala and M. Leskela in “Atomic Layer Deposition” in Handbook of Thin Film Materials, H. S. Nalwa, Editor, Academic Press, San Diego, 2001, Volume 1, Chapter 2. Such films, especially metal and metal oxide films, are critical components in the manufacture of electronic circuits and devices.
In an ALD process for depositing copper films, a copper precursor and reducing agent are alternatively introduced into a reaction chamber. After the copper precursor is introduced into the reaction chamber and allowed to adsorb onto a substrate, the excess (unabsorbed) precursor vapor is pumped or purged from the chamber. This is followed by introduction of a reducing agent that reacts with the copper precursor to form copper metal and a free form of the ligand. This cycle can be repeated if needed to achieve the desired film thickness.
This process differs from chemical vapor deposition (CVD) in the decomposition chemistry of the metal complex. In a CVD process, the complex decomposes on contact with the surface to give the desired film. In an ALD process, the complex is not decomposed on contact with the surface. Rather, formation of the film takes place on introduction of a second reagent, which reacts with the deposited metal complex. In the preparation of a copper film from a copper(II) complex, the second reagent is a reducing agent.
To be useful in an ALD process, the copper complex must be volatile enough to be sublimed without thermal decomposition. Typically, trifluoromethyl group-containing ligands have been used to increase the volatility of the copper complexes. However this approach has drawbacks in the preparation of interconnect layers, since halides adversely affect the properties of the interconnect layer.
The ligands used in the ALD processes must also be stable with respect to decomposition and be able to desorb from the complex in a metal-free form. Following reduction of the copper, the ligand is liberated and must be removed from the surface to prevent its incorporation into the metal layer being formed.
U.S. Pat. No. 5,464,666 describes the decomposition of 1,3-diimine copper complexes in the presence of hydrogen to form copper. This patent also describes the use of 1,3-diimine copper complexes in a Chemical Vapor Deposition process for producing copper-aluminum alloys.
DE 4202889 describes the use of 1,3-diimine metal complexes to deposit coatings, preferably via a Chemical Vapor Deposition process. Decomposition of the metal complexes in a reducing atmosphere, preferably hydrogen, is disclosed.
S. G. McGeachin, Canadian Journal of Chemistry, 46, 1903–1912 (1968), describes the synthesis of 1,3-diimines and metal complexes of such ligands.
N. A. Domnin and S. I. Yakimovich, Zh. Organ. Khim, 1965, 1(4), 658, describe the reaction of aliphatic beta-diketones with unsymmetrical N,N-dialkylhydrazines to produce bis(dialkylhydrazones).